This paper reviews optical fiber amplifiers such as Erbium doped fiber amplifiers EDFAs, many types of Raman amplifiers RAs. Thulium doped fiber amplifiers, Tellurite-based fiber Raman amplifiers, semiconductor optical amplifiers and fiber optic parametric amplifiers, principle of operation and construction. As these amplifiers are used for optical fiber communication projects so the authors shall go through their main characteristics which are amplifier gain and span length, wavelength bandwidth and noise. Current repeater spacing and speed of EDFA is in the range of 80-100 Km and 40 Gb/s while those for RA is in the range of 100-160 Km and 160-320 Gb/s. Each type of amplifier is suitable for certain application depending on these characteristics. In metro/access networks there are many add/drop locations resulting in high loss, coarse wavelength division multiplexing with about 20 nm separation between each channel as with this principle cheap multiplexing and laser transmitters are used.